1. Field of Invention
The present invention relates to a piezoelectric printhead and its method of manufacture. More particularly, the present invention relates to a piezoelectric printhead that uses a metallic layer and a thick film layer with a slot hole therein instead of conventional ceramic material to form a vibration layer and an ink cavity layer structure.
2. Description of Related Art
In general, the operating mechanism of a conventional ink-jet printer can be classified into thermal bubble and piezoelectric. Thermal bubble ink-jet printing utilizes a heater to vaporize an ink drop quickly to form a high-pressure gaseous ink bubble so that the ink is suddenly ejected from an ink nozzle. Because thermal bubble print head is inexpensive to produce, they are mass-produced by commercial companies such as HP and Canon. However, the high-temperature vaporization mechanism needed to operate the printhead often limits the type of ink (mainly a water-soluble agent) that can be selected. Such limitations narrow its field of applications.
Piezoelectric printing utilizes the deformation of a block of piezoelectric ceramic material when a voltage is applied. Such deformation compresses liquid ink and creates a liquid jet out from an ink reservoir. Compared with a thermal bubble type of print head, a piezoelectric printhead has several advantages. Unlike a thermal bubble printhead that demands the ink to be vaporized at a high temperature and hence may change the color somewhat, the piezoelectric printhead has no such problem. Furthermore, the piezoelectric printhead operates without cyclic heating and cooling and hence may have a longer working life. Moreover, the piezoelectric ceramic material responds to a voltage quickly and hence may produce print documents a lot faster. The response of a thermal bubble printhead, on the other hand, is limited by the rapidity of heat conduction. Last but not least, the amount of deformation in the piezoelectric ceramic depends on the voltage of the electricity applied. In other words, by controlling the voltage applied to the piezoelectric ceramic, size of the ink droplet ejected from a nozzle may change. Ultimately, quality of the document produced by the piezoelectric printhead can be improved.
FIG. 1 is a schematic cross-sectional view of a conventional piezoelectric ink-jet print head. Ceramic green tapes for forming a conventional piezoelectric ink-jet print head 100 including an upper electrode layer 102, a piezoelectric layer 104, a lower electrode layer 106, a vibrating layer 108, an ink cavity layer 110 and an ink cavity bottom film layer 112 are manufactured in thick film processes. Thereafter, the green tapes are pressed together in the correct order and fired to form a ceramic structure such as the piezoelectric ink-jet printhead manufactured by EPSON.
To operate the piezoelectric printhead 100, a voltage is applied to the piezoelectric layer 104 through the upper electrode 102 and the lower electrode 106. Since the piezoelectric layer 104 is a piezoelectric ceramic material, the piezoelectric layer 104 will deform pushing the vibrating layer 108 and pressuring the ink inside the ink cavity 114. A portion of the pressurized ink ejects from an ink nozzle 116 and travels to a paper document to form a dot pattern.
In a conventional piezoelectric ink-jet printhead, aside from the metallic upper electrode and the lower electrode, other layers are separately formed in thick film ceramic processes and then combined together by pressure and high-temperature treatment. Consequently, a conventional piezoelectric ink-jet printhead has the following disadvantages: 1. Since the piezoelectric ink-jet printhead has a relatively small dimension but a relatively high precision, various thick ceramic films must be carefully aligned before being joined together. This may lead to a lowering of product yield. 2. Because the piezoelectric printhead has a relatively complicated structure, the ceramic material may shrink unevenly during a thermal treatment process leading to stress or structural damage. Again, this may lead to a drop in product yield. 3. The uneven shrinkage due to a high temperature treatment may also lead to a mismatch between delicate parts within the ink-jet printhead. This aspect of the production not only lowers product yield, but also decreases the packing density of ink-jet printheads leading to a lower print resolution.